How should estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status be assessed and used to guide treatment in breast cancer?

Hormone Receptor Status in Breast Cancer: ER, PR, and HER2

All invasive breast cancers must have ER, PR, and HER2 status determined through immunohistochemistry (IHC) and/or in situ hybridization testing, as these biomarkers are the only validated markers that directly guide treatment decisions and impact mortality and quality of life. 1, 2, 3, 4

Essential Testing Requirements

What Must Be Tested

• ER status: Required for all ductal carcinoma in situ (DCIS) and all invasive breast cancers 1, 2, 1
• PR status: Required for all invasive breast cancers 1, 2, 1
• HER2 status: Required for all newly diagnosed invasive breast cancers 1, 2, 1, 3

When to Test

• Core needle biopsy is mandatory before any treatment is initiated to ensure diagnosis of invasive disease and assess biomarkers 3
• Testing should be performed on the initial diagnostic specimen with proper fixation to ensure optimal antigen preservation 3
• Retesting is required on metastatic lesions when disease recurs, as receptor status may change (discordance occurs in 9-12% of cases) 5, 4, 6

Testing Methodology

ER and PR Assessment

• IHC is the standard method for determining ER and PR status 1, 2, 7
• Laboratories must validate their assay against clinically validated methods with ≥90% concordance for positive results and ≥95% concordance for negative results 7
• Positive threshold: ≥1% of tumor cells with nuclear staining is considered positive per ASCO/CAP guidelines 7, 4
• Standardized scoring systems (Allred score or H-score) should be used 3, 8

HER2 Assessment

Six FDA-approved methods exist for HER2 testing: 1, 2, 1

1. IHC HercepTest (DAKO)
2. IHC Pathway HER2 test (Ventana)
3. INFORM HER2 FISH test (Ventana)
4. PathVysion HER2 FISH test (Vysis)
5. PharmaDX HER2 FISH test (DAKO)
6. SPOT-Light HER2 CISH test (Invitrogen)

HER2-positive criteria (updated ASCO-CAP 2013): 3

• IHC 3+ when >10% of cells (not 30%) show complete membrane staining
• FISH positive if HER2 gene copies ≥6 or HER2/chromosome 17 ratio ≥2.0

Equivocal results require reflex testing: 1, 2, 9

• IHC 2+ requires FISH confirmation
• FISH ratios 1.8-2.2 or gene copies 4-6 require additional testing with alternative method
• Never treat equivocal HER2 as negative without confirmatory testing 9

Laboratory Quality Requirements

Accreditation and Validation

• Only accredited laboratories should perform ER, PR, and HER2 testing 1, 2
• Laboratories must have standardized testing procedures and proficiency evaluation programs 1, 2
• Initial validation requires 95% concordance with clinically validated assays 1, 2, 7

Common Sources of Error

• Interlaboratory variability: ER and PR reliability varies widely among laboratories due to diverse methodologies 1, 2
• False-positive and false-negative HER2 results are common in clinical practice 1, 2
• Decalcification of bone biopsies can affect IHC results, particularly for PR (33% major discrepancy rate) 10
• Tumor heterogeneity may cause sampling errors and discordant results 4

Clinical Application

Treatment Decisions Based on Receptor Status

ER/PR-positive disease: 5, 4

• Determines eligibility for endocrine therapy (tamoxifen, aromatase inhibitors)
• Endocrine therapy is first-line for metastatic disease unless visceral crisis

HER2-positive disease: 5, 4, 11

• Determines eligibility for HER2-targeted therapies (trastuzumab, pertuzumab, T-DM1, lapatinib)
• Requires dual HER2 blockade (trastuzumab + pertuzumab) with chemotherapy for metastatic disease

Triple-negative disease (ER-/PR-/HER2-): 3, 4

• Chemotherapy is primary systemic treatment option
• Consider BRCA testing for PARP inhibitor eligibility

Managing Discordant Results

When primary and metastatic receptor status differ: 5, 4

• Use the receptor status from the metastasis to direct therapy (ASCO panel informal consensus)
• Consider clinical scenario and patient's goals for care
• True biologic change versus tumor heterogeneity versus assay variability cannot always be differentiated

Pathology Report Requirements

Essential elements that must be included: 1, 2

• Tumor site and specimen type
• Histologic type and grade
• ER status with percentage of positive cells
• PR status with percentage of positive cells
• HER2 status (IHC score or FISH ratio/gene copies)
• Fixation method and time
• Up to 50% of pathology reports are missing critical elements 1, 2

Critical Pitfalls to Avoid

• Do not proceed with treatment if ER, PR, or HER2 results are missing or equivocal without resolution 9
• Do not assume receptor status remains unchanged at recurrence—always retest metastatic lesions 5, 4
• Do not use non-validated or non-FDA-approved tests for treatment decisions outside clinical trials 5, 4
• If ER/PR/HER2 are negative on core biopsy, retest on surgical specimen to account for tumor heterogeneity 3
• Ensure proper specimen orientation and communication between clinician and pathologist about biomarker testing requests 1, 2